Smart NFC tags are seeing many interesting applications and can benefit from further miniaturization. A passive temperature sensing tag with 5.1 mm diameter is demonstrated, comprising a thin-film microfabricated antenna and an NFC chip. The microantenna/coil comprises two 15 µm-thick electroplated copper layers embedded in SU-8, withstanding the soldering process of a BGA NFC IC. The µ-antenna design challenge is to miniaturize while minimizing performance impairment (inductive-coupling distance), while the micromachining process is very dependent on topography propagation. Fabricated coils were successfully characterized (2.32 µH inductance; 13.76 MHz self-resonance) and temperature was read (after assembly) with a mobile phone at distances of up to 7 mm.
